Method of and apparatus for screening paper pulp



April 25, 1950 w, YOUNG ET AL 2,505,513

METHOD OF AND APPARATUS FOR SCREENING PAPER PULP Filed Feb. 1, 1944INVENTOR. I FRANK W. YOU/VG 5y JVf/Y4F4HL6ZQf/Y fiTTOR/VEYS PatentedApr. 25, 1950 METHOD OF AND APPARATUS FOR SCREENING PAPER PULP Frank W.Young, Medfield, and Sven A. Fahi ren, Wrentham, Mass, assignors to BirdMachine Company, South Walpole, Mass, a corporation of MassachusettsApplication February 1, 1944, Serial No. 520,608

3 Claims.

1 This invention relates broadly to the removal of chips and knots, ofwood, from raw paper pulp stock, although not so limited. Moreparticularly. the invention relates to the prevention of troublesomefoam in the instrumentality utilized to remove or separate the chips andknots from the paper pulp.

* Paper pulp, manufactured from wood by any of the several chemicalprocesses contains chips and knots. Such chips and knots are removed byvarious types of screens and so-called knotters. Most chemical pulps,such as those of the soda and sulphate types, as they come from thedigesters, contain a foam producing liquor. It would be desirable,therefore, to wash the pulp free of such liquor before it is screened orknotted in-order to prevent the occurrence of foam in the knotterbecause such foam is often so troublesome that the operation of theknotter is difficult, if not impossible. On the other hand, the washingof the pulp is seriously hindered by the presence of chips and knots sothat it would be of great advantage to screen and knot the stock be forewashing.

It is therefore an object of this invention to screen and knot the rawunwashed stock without producing foam. It is to be understood thatbubbles or foam are produced when air becomes mixed with soapy liquor.Consequently, if air is eliminated or prevented from entering the soapyliquor, the foam is not formed. It is, therefore, a further object ofthe invention to so operate the knotter that air will not be mixed withthe liquor flowing to and through the knotter. Accordingly the stock isintroduced into the liqnor fed to the knotter below the level of suchliquor.

Yet another object of the invention is a practical instrumentality bywhich to introduce the stock into the liquor in the knotter. To thisend, the stock is introduced into the knotter box through a spoutdisposed below the level of liquid in the box.

The invention also seeks a method of an appsratus for screening unwashedstock without troublesome foam and at a relatively high consistency inthe interest of relatively high capacity, relatively high pulpconsistency, ease and convenience of operation and compactness ofinstallation.

These and other objects of the invention and the means for theirattainment will be more apparent from the following detaileddescription, taken in connection with the accompanying drawion,illustrating one embodiment by which the 2 invention may be realized andin which the annexed drawing is a somewhat diagrammatic view showing ablow tank from which the stock is delivered directly to theinstrumentality in which tne knots and chips are separated from the raws ock.

Referring to the drawing, it will be understood that the stock is blownfrom the digester (not shown) through the pipe 3 to the blow tank 5 at,say. about 12% consistency. It is diluted with black liquor enteringfrom pipe I in the conical bottom 8 to about, say, 4% to 6% consistency.This consistency is regulated and maintained by the power input to themotor 9 which drives the agitator l l.

The stock, containing the chips and knots l2, and at, say, 5%consistency, is pumped by pump l3 from the blow tank 5 through pipe to aspout or nozzle I5 disposed above a screen 20 but with its open mouthsubmerged below the level is of the liquor, Thus no air is permitted tomix with the stock emerging from the spout l5 and the spout is shown asof progressively increasing diameter whereby turbulence is prevented andthus bubbles and foam are not formed.

In the illustrated embodiment, the screen box ill and trough l8 areillustrated as taking, generally, the form of the screen shown in UnitedStates Patents Nos. 2,222,146 and 2,293,978, although the method of thisinvention is not dependent for its utility upon the use of such screenbox and trough since any screen serving the purpose is within thepurview of the invention. In the illustrated embodiment, the screen 2|]is 1 formed with an upwardly inclined or otherwise exposed orunsubmerged screen portion 2i and is so mounted as to be capable ofagitation or vibration. Spring suspension devices for the knotter box Hmay take the form shown in the patents and are schematically indicatedat 23 and which are mounted in fixed position and connected as by pin 39to the side wall of the box ill. The knotter box may be agitated by anyconvenient vibrating device, for instance, the eccentric connectionindicated schematically at 25, which may be operated by motor means, notshown, as in the patents.

The chips and knots which enter the knotter box I] from the nozzle l5travel along the unsubmerged portion of the screen and are here shown astravelling up the inclined portion 2| of the screen plate as the resultof the vibratory action of the screen plate 20 and are discharged overthe end of the screen 20 and into, say, the conduit 28 by which they areevacuated. The screened 3 stock, free of chips and knots (known asaccepted stock), passes through the screen plate- 24 and falls into thelower portion of the trough II from which, contrary to the practice ofthe patents, it flows through the outlet 30 and pipe 32 into thecompartment 33 where it is preferably diluted to about 1% consistency byliquor entering through pipe 35. The liquid level 34 in compartment 33,which regulates or controls the liquid level I9 in the knotter l1, I8 ismaintained by controlling the flow of fluid in the outlet, here shown asby a float 38 controlling the outlet valve 35 in the conduit 31, bywhich the diluted stock is conducted to any type of pulp washer, notshown. Here, again, the outgoing accepted stock is conducted in aconstant steady flow without the opportunity to become aerated and hencethe formation of foam at this point is also avoided.

Various modifications will occur to those skilled in the art in theconfiguration and disposition of the component elements going to make upthe invention as a whole as well as in the several features thereofcapable of separate use and for other purposes, and no limitation isintended by the phraseology cf the foregoing description orillustrations in the accompanying drawings excent as indicated in theappended claims.

What is claimed is:

1. The method of screening knots and chips from paper pulp with freedomfrom troublesome foam which comprises feeding the pulp through adownwardly and outwardly inclined conduit formed with a bell-shapedsubmerged end disposed immediately above a vibrating submerged screen tothereby prevent the admission of air to the paper pulp fed to thescreen.

2. The method of screening knots and chips of the soda and sulphatetypes with freedom from troublesome foam which comprises feeding thepulp through a downwardly and outwardly inclined conduit whereof themouth is closely positioned to a curvilinear screen secured at its oneend to an end of the knotter box and whereof its other end extendsupwardly whereby 45 onthcvibrationofthescreentheknotaare caused totravel up the screen and are discharged over the end wall'of the knotterbox.

3. Apparatus for treating paper pulp of a consistency in excess of 2%,comprising a screen, means to control the level of liquid to apredetermined elevation above the area of the screen and means tointroduce stock into the liquid above the screen at a level below thelevel of the liquid.

- FRANK W. YOUNG.

BVEN A. FAHLGREN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Control of Beater Furnish toEliminate Foaming on Paper Machines, Technical Association Papers,Series XI, pp. 57 and 58, (1928).

A Survey of Pitch Troubles in the Manufacture and Use of Sulphite Pulp.Technical Association Papers, Series XIX, p. 189, 1936.

The Manufacture of Pulp and Paper, v01 IV, section 7, p. 29, 1928.

